1. Field of the Invention
The present invention relates to the combination of an electrical motor and generator, and more particularly to a single device which performs both motor and generator functions.
2. Discussion of Related Art
In general, an electric motor can be operated as a generator and vice versa. These functions of a motor or a generator can be selected by whether power is delivered to the unit from an external source of electrical power or whether the unit is mechanically driven by an external source of mechanical energy such as an internal combustion engine in an automobile which would allow the unit to act a generator to supply electrical energy.
The subject invention comprises a structure particularly adapted for automotive applications which permits the combination of the starter motor function and the generator (generic DC or AC) or alternator (AC) function in a unique package to take advantage of the motor/generator characteristics described above. The subject invention is physically located at a position between the internal combustion engine and the transmission in the drive train of an automobile, making use of either the flywheel or the torque converter as part of the system. This is in contrast to the traditional location of a separate starter motor which is momentarily conventionally connected to the flywheel on the engine during the cranking or starting cycle, and the traditional location of a separate generator or alternator which is belt driven from the crankshaft of the engine. Since these functions of the starter and alternator are combined, the unit may be located in line between the engine and transmission thereby eliminating the requirement for being belt or gear driven and to take advantage of the fact that only one motor/generator unit will be used in place of two units as in present conventional use.
Various approaches in producing a dual purpose starter generator machine for use on motor vehicles have been developed since the early 1900's. For example, U.S. Pat. No. 1,250,718 issued to Turbanyne, Dec. 18, 1917 discloses a DC motor/generator having a rotating armature that is ring wound. When operated as a DC motor, DC current is supplied to the rotor through conventional commutator brushes.
Another starter generator is disclosed in U.S. Pat. No. 1,325,677 issued to Midgley, on Dec. 23, 1919. In this design, a conventional DC machine having a wound rotor is fitted with four brushes on the commutator ring. One of these brushes is movable away from the commutator. Movement of the movable brush serves to engage or disengage an automatic circuit as a voltage regulation device when the machine is operated as a generator. When operated as a DC motor, the movable brush effectively disengages the automatic circuit by connecting the circuit across two brushes of the same polarity.
Another example of a starter generator machine is disclosed in U.S. Pat. No. 2,184,236 issued to Heintz on Dec. 19, 1939. In this machine, in addition to conventional slip rings and brushes for energizing the windings on the rotor during generator and motor operation, the rotor is fitted with rotatable brushes. These rotatable brushes are in engagement with a stationary commutator which feeds low voltage direct current to the stator windings during the engine cranking operation. The rotating brushes are moved out of engagement with the commutator by centrifugal force as the engine crank shaft is accelerated. Thus in this design, the rotatable brushes provide the rotating stator magnetic field for operation of the device as a motor. When operating as a generator, the Heintz device produces alternating current.
In a more recent starter motor alternator disclosed in U.S. Pat. No: 4,219,739 issued to Greenwell on Aug. 26, 1980, the main rotor winding is connected in series with the main stator winding. In addition, the exciter armature winding is on the rotor, and exciter field winding is on the stator. During starter motor operation, the main rotor winding is connected in series with the starter field winding through a commutator and conventional DC brushes. During alternator operation, the brushes are lifted off the commutator and the exciter armature winding slip rings are connected to the main rotor winding.
In all of the above examples, external current is fed through a commutator to the windings on the rotor. The current carried by the conductor in the magnetic field produces a torque which causes rotation of the machine as a motor. When operated as generator or alternator, current is once again fed through a commutator or slip rings to windings on the rotor to provide excitation. These dual purpose motor generator sets have a variety of disadvantages. In any conventional dual purpose machine, certain sacrifices must be made in order to accommodate both generator and motor functions in a single device as compared to single purpose machines. For example, previous and conventional motor generator designs for use in a motor vehicle such as an automobile or an aircraft have a low power to size ratio, are relatively costly, and have a high length to diameter ratio. In fact, it has therefore been impractical to develop a combined motor generator design for use in automobiles.
The dual purpose machine concept has primarily been utilized in aircraft design. However, these machines are extremely complex to manufacture with resultant high cost. Because of the power requirements, overall size, and complexity of a conventional motor generator or dual starter motor alternator of conventional design, automotive vehicles utilize separate starter motors and alternators.
The disadvantages of conventional starter motor designs include very high noise during operation, a low electromechanical efficiency, relatively large size requirements, high motor weight and battery size requirements, and low reliability. In addition, the necessity for having a separate alternator increases the overall space allocation to these functions.
It is an object of the present invention to provide a motor generator unit having a flat nonmagnetic ironless stator and a magnetic flux return path fixed with respect to the magnets.
It is another object of the present invention to provide an alternator starter which replaces the ring gear located between the engine and transmission of a conventional motor vehicle.
It is another object of the present invention to provide an alternator starter adaptable to conventional drive train designs.
It is another object of the invention to provide an alternator starter having a thin, nonmagnetic ironless stator assembly. An ironless stator assembly means that there are no iron losses in the stator. Only IR losses are present. Therefore total losses are minimized.
It is a further object of the invention to provide an alternator starter having no bearings, the alternator starter being integral with the power shaft of the internal combustion engine.
It is a further object of the invention to provide an alternator starter for an automotive vehicle having a high efficiency per unit weight ratio and a high output per unit weight ratio.
It is a still further object of the invention to provide an alternator starter in an automotive vehicle which generates no starting noise, has high reliability, high efficiency, and requires a minimal amount of space within the conventional drive train assembly.
It is a still further object of the present invention to provide an alternator starter having a twenty four pole design for sensing the rotational position of 2, 4, 6, 8 or 12 cylinder engines.
It is a still further object of the invention to provide a stator winding structure comprised of flat metal stampings in a single winding structure.